Inverted-trench grounded-source FET structure using conductive substrates, with highly doped substrates

ABSTRACT

This invention discloses an inverted field-effect-transistor (iT-FET) semiconductor device that includes a source disposed on a bottom and a drain disposed on a top of a semiconductor substrate. The semiconductor power device further comprises a trench-sidewall gate placed on sidewalls at a lower portion of a vertical trench surrounded by a body region encompassing a source region with a low resistivity body-source structure connected to a bottom source electrode and a drain link region disposed on top of said body regions thus constituting a drift region. The drift region is operated with a floating potential said iT-FET device achieving a self-termination.

This Patent Application is a Divisional Application and claims thePriority Date of application Ser. No. 12/653,354 filed on Dec. 11, 2009,now U.S. Pat. No. 8,053,834 and application Ser. No. 12/653,354 is aDivisional Application of application Ser. No. 11/500,810 filed on Aug.8, 2006 by common Inventors of this Application. The application Ser.No. 11/500,810 is now issued into U.S. Pat. No. 7,633,120. TheDisclosures made in the patent application Ser. Nos. 12/653,354 and11/500,810 are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the semiconductor power devices. Moreparticularly, this invention relates to an inverted-trench groundedsource field effect transistor (FET) structure that uses a conductivesubstrate with highly doped P+ substrate.

2. Description of the Prior Art

Conventional technologies to further reduce the source inductance forsemiconductor power devices including the source inductance in FET,MOSFET and JFET devices are challenged by several technical difficultiesand limitations. Specifically, there are technical challenges faced bythose of ordinary skill in the art to reduce the source inductance.Meanwhile, there are ever increasing demand to reduce the sourceinductance in the semiconductor power devices because more and morepower devices are required for applications that demand these devices tofunction with high efficiency, high gain, and high frequency. Generally,reduction of source inductance can be achieved by eliminating thebond-wires in the package of a semiconductor power device. Many attemptsare made to eliminate the bond-wires by configuring the semiconductorsubstrate as a source electrode for connection of the semiconductorpower devices. There are difficulties in such approaches due to thefacts that typical vertical semiconductor power devices is arranged toplace the drain electrode on the substrate. Referring to FIGS. 1A and 1Bfor the vertical power devices shown as trenched and planar DMOS devicesrespectively that uses the substrate as the drain electrode with thecurrent flows vertically from the source down to the drain regiondisposed at the bottom of the substrate. The top source electrodeusually requires bond wires for electrical connections during a devicepackaging process thus increasing the source inductance.

Other packaging technologies such as flip chip packaging can be appliedin some instances. However, when applying a flip chip configuration to avertical DMOS with the drain contact brought to the top surface. Thedrain contact and the gate pad are both disposed on the top surface andthat results in drawbacks due the large dies that leads to increasedprocessing cost and complexity. Furthermore, there are extra processingcosts for the formation of solder balls or solder pillars on the topside of the device, particularly for CMOS or LDMOS style planar devices.

Referring to FIG. 1C for a new vertical channel LDMOS device disclosedby Seung-Chul Lee et al, in Physica Cripta T101, pp. 58-60, 2002, with astructure shown as a standard vertical trenched DMOS wherein the draincontact is disposed on the side while the source is still on top of theactive area. However, this device has a limitation due to a large cellpitch caused by the lateral spacing required by the top drain contact.In addition to the limitation of large cell pitch, the trenched FETdevice in general has a fabrication cost issue due to the fact that thetrenched FET requires technologies that may not be available in allfoundries and that tend to drive up the fabrication costs. For thisreason, it is also desirable to implement the power device as lateraldevice with planar gate.

Several lateral DMOS with grounded substrate source have been disclosed.A lateral DMOS device typically includes a P+ sinker region (oralternate a trench) to connect the top source to the P+ substrate. Thesinker region or the trench increases the pitch of the cell due to thedimensions occupied by the sinker or the trench. Referring to FIG. 1Dfor a device cross section disclosed by G.Cao et.al, in “ComparativeStudy of Drift Region. Designs in RF LDMOSFETs”, IEEE Electron Devices,August 2004, pp 1296-1303.Ishiwaka O et al; disclose in “A 2.45 GHzpower Ld-MOFSET with reduced source inductance by V-groove connections”,International Electron Devices Meeting. Technical Digest, Washington,DC, USA, 1-4 Dec. 1985,pp. 166-169. In U.S. Pat. No. 6,372,557 by Leong(Apr. 16, 2002) attempts are made to use a buried layer at the interfaceof the P+ and P-epi layers to reduce the lateral diffusion and hencereduce pitch. In U.S. Pat. No. 5,821,144 (D'Anna and Hébert, Oct 13,1998) and U.S. Pat. No. 5,869,875, Hébert “Lateral Diffused MOStransistor with trench source contact” (issued on Feb.9, 1999) devicesare disclosed to reduce the cell pitch by placing the source sinker ortrench on the OUTER periphery of the structure. However, in thesedisclosures, most of the devices as shown use the same metal over thesource/body contact regions and gate shield regions and some of thedevices use a second metal for drain and gate shield regions. Theseconfigurations generally has large cell pitch due to the lateraldiffusions that increases the drift length over the horizontal plane. Alarge cell pitch causes a large on-resistance that is a function ofresistance and device areas. A large cell pitch also increases thedevice costs due to a larger size of the device and a larger sizepackage.

Therefore, a need still exists in the art of power semiconductor devicedesign and manufacture to provide new device configurations andmanufacturing method in forming the power devices such that the abovediscussed problems and limitations can be resolved.

SUMMARY OF THE PRESENT INVENTION

It is therefore an aspect of the present invention to provide a new andimproved inverted ground-source trenched FET on highly doped substrate,e.g., highly doped P+ substrate, with a bottom-source and top-drainhaving a reduced cell pitch thus achieving low manufacturing cost. Thelow manufacturing cost is achieved because a low effective die cost witha reduce cell pitch when the improved device configuration isimplemented. The above discussed technical difficulties and limitationsof not able to shrink the cell pitch as encountered in the conventionalsemiconductor power devices are therefore overcome.

Specifically, it is an aspect of the present invention to provide a newand improved inverted ground-source trenched FET on highly dopedsubstrate, e.g., highly doped P+ substrate, with a bottom-source andtop-drain that has a significant reduce source inductance by eliminatingthe source wires and meanwhile minimizing the specific on resistance Rspby using an integrated body-source short structure at the lower portionof the trenches surrounded by the gate electrodes.

It is another aspect of the present invention to provide a new andimproved inverted ground-source trenched FET on highly doped substrate,e.g., highly doped P+ substrate, with a bottom-source and top-drain thatare scalable for compatible with applications over a range of high andlow voltages. The semiconductor power devices as disclosed in thisinvention further achieve rugged and reliable performance with reducedpossibility of latch up, reduced hot carrier injection and peak voltagegeneration away from gate oxide, etc. because of the distributed bodycontact configurations.

It is another aspect of the present invention to provide a new andimproved inverted ground-source trenched FET on highly doped substrate,e.g., highly doped P+ substrate, with a bottom-source and top-drain thatare scalable for providing a vertical current channel with controllabledrift region length such that it is more adaptable for pitch reductionconfigurations. The bottom source connection is established through aconductive substrate and a source contact formed at the bottom of thetrench in direct contact with the highly doped substrate. Therequirement for using a deep resistive sinker or a trench contact istherefore eliminated.

It is another aspect of the present invention to provide a new andimproved inverted ground-source trenched FET on highly doped substrate,e.g., highly doped P+ substrate, with a bottom-source and top-drain withreduced gate-drain capacitance by forming a thicker oxide layer over thedrain extension to reduce the drain-to-gate capacitance Cgd to increasethe break down voltage (BV).

It is another aspect of the present invention to provide a new andimproved inverted ground-source trenched FET on highly doped substrate,e.g., highly doped P+ substrate, with a bottom-source and top-drain withthe termination region formed outside the continuous gate ringstructure. In a preferred embodiment, a typical layout of this structureis based on a closed cell configuration. The N-drift region in thisconfiguration is left unconnected because there is no contact to thetermination region. Since the substrate is at the source potential thatis ground potential for an NMOS device, the floating N-drift region islikely operates at a ground potential to provide a self-termination. Thedevice configuration further has an advantage that any damage from thesawing of the dies in the scribing region will tend to short thefloating N-drift regions to the grounded substrate.

Briefly in a preferred embodiment this invention discloses asemiconductor power device constituting an inverted ground-sourcetrenched FET on highly doped P+ substrate with a bottom-source andtop-drain that further includes a plurality of trenches for forming agate therein. The semiconductor power device further includes abody-source contact disposed on the bottom of the trenches isolated fromthe trenched gate for electrically connecting a body region to a sourceregion on the highly doped P+ substrate.

Furthermore, this invention discloses a method for manufacturing aniT-FET semiconductor device. The method includes a step of forming asource on a bottom and a drain on a top surface of a semiconductor andforming a trenched gate as a gate layer attached to trench sidewalls forcontrolling a vertical channel along the trenched gate in thesemiconductor substrate. The method further includes a step of formingthe trenched gate to fully surround the source and drain all sideswhereby the iT-FET device achieving a self-termination.

These and other objects and advantages of the present invention will nodoubt become obvious to those of ordinary skill in the art after havingread the following detailed description of the preferred embodiment,which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross sectional views for showing the typicalvertical power device configurations implemented as a trenched-gate andplanar-gate vertical power devices respectively.

FIG. 1C is a cross sectional view of vertical channel LDMOS device.

FIG. 1D is a cross sectional view of a drift region design in a LDMOSFETdevice for RF application.

FIG. 2 is a cross sectional view of an inverted ground-source trenchedFET device with body-source short structure formed on the bottom of atrench distributed within the device as an embodiment of this invention.

FIG. 3 is a cross sectional view of another inverted ground-sourcetrenched FET device with body-source short structure formed on thebottom of a trench distributed within the device as and a thicker oxideover the drain extension to reduce the Cgd and increase BV as anotherembodiment of this invention.

FIG. 4 is a cross sectional view of another inverted ground-sourcetrenched FET device with body-source short structure formed as anintegrated gate shield to reduce the parasitic capacitance as anotherembodiment of this invention.

FIGS. 5A to 5T are a series of cross sectional views to illustrate themanufacturing processes implemented in this invention to manufacture adevice as shown in FIG. 2.

DETAILED DESCRIPTION OF THE METHOD

Referring to FIG. 2 for a cross sectional view of an N-channel invertedground-source trenched FET device with a bottom source and a top drainof this invention. The inverted ground-source trenched N-channel FETdevice is supported on a P+ substrate 105 functioning as a bottom sourceelectrode. Alternatively a P-channel device may be formed over an N+ Sisubstrate or other substrate such as silicon carbide, GaN, or otherkinds of semiconductor substrates, etc. A layer of P− epitaxial layer110 is supported on top of the substrate 105. The substrate isconfigured with an active cell area and a termination area typicallydisposed on the peripheral of the substrate. The FET device 100 has aplurality of trenches opened from the top surface of the substrate toreach to a lower portion of the epitaxial layer 110. The trenches openedin the active cell area is wider to form a gate with gate polysiliconlayer attached to the sidewalls of the trench with the sidewalls of thetrenches padded with a trench wall oxide layer 125 and the centralportion filled with an insulation material, e.g., a BPSG layer 125′. Atrench of a narrower width is formed in both the termination area orwithin the active area to form the gate runner 120′ with trenchedsidewall gate 120 from the active area to the termination area. A P-bodyregion 130 is formed in the epitaxial layer surrounding the insulatedtrenched sidewall gate 120. An N-link region 135 is formed on top of thebody region 130 to contact a N-drift region 145 encompassed a N+ draincontact region 140 near the top surface of the substrate. A surfaceblanket N type implant layer 142 is optional.

The trenched vertical FET device further includes a body-source shortstructure formed at the bottom of the trenches in the active cell area.The body-source short structure is formed with a conductive plug 150,e.g., a silicide of Ti, Co, W plug, surrounded by a highly doped N+region 155 and a highly doped P++ region 160 below the conductive plug150 to form a highly conductive low resistivity body-source shortstructure. A drain metal covers 170 the active cell area and a gatemetal 180 is formed in the termination area. The drain metal and thegate metal are in electrical contact with the drain 140 and the gaterunner 120′ through a drain contact opening and gate contact openingopened through the dielectric layer 175, e.g., a BPSG layer, and aninsulation layer, e.g., an oxide layer 165, covering the top surface ofthe FET device. The integrated body/source short 150 as shown isdistributed throughout the device. The device structure provides avertical channel that includes a bottom source with the source connectedto the bottom of the substrate. Unlike the conventional bottom sourcedevices, the bottom source devices of this invention are implementedwithout using a P+ sinker immediately below the source region. Instead,the bottom source device of this invention employs an embedded sourceand body with the source/source short structure 150. Therefore, thedevice structure of this invention saves the lateral space and avoidsthe lateral diffusion for the P+ sinker.

Referring to FIG. 3 for an alternate embodiment of an invertedground-source trenched FET device that has a similar configuration asthat shown in FIG. 2. A thicker oxide layer 165′ formed over the drainextension to reduce the drain-to-gate capacitance Cgd to increase thebreak down voltage (BV). The gate contact region in the termination areais shown with a thicker oxide layer 165′. The trench is narrower andfilled with the gate polysilicon layer 120′. The gate metal 180 isformed the same time as the drain metal 170 is formed then patternedinto the drain metal and the gate metal on the top surface of the devicewith the source electrode formed at the bottom of the substrate servingas a ground electrode.

A typical layout of this structure is based on a closed cellconfiguration. The N-drift region OUTSIDE of the active cell in thisconfiguration is left unconnected because there is no contact to thetermination region. Since the substrate is at the source potential thatis ground potential for an NMOS device, the floating N-drift region 145is likely operates at a ground potential. The device configuration asshown further has an advantage that any damage from the sawing of thedies in the scribing region will tend to short the floating N-driftregions to the grounded substrate. The structure is thereforeself-terminated, eliminating the need for complex termination schemessuch as floating rings, junction-termination-extensions, field plates,etc, that are typically required for prior-art vertical planar andTrench-MOSFET structures.

Referring to FIG. 4 for an alternate embodiment of an invertedground-source trenched FET device that has a similar configuration asthat shown in FIG. 3. The only difference is the body-source shortstructure is now formed as an integrated gate shield 150′ that extendedfrom the top of the substrate into the bottom source layer 105 tocontact the highly doped P++ regions 160. This integrated gate shield tofunction as the source-body short structure further reduces theparasitic capacitance.

The body-source short structure 150 as shown in FIGS. 2-4 is formed ineach active cell to connect the source region 155 to the bottom sourceelectrode disposed on the bottom of P+ substrates. Alternatively anN-channel device may be formed over an N+ substrate and such device doesnot need to have the body-source short in every cell, all over theactive area, since the source will automatically connect to the N+substrate

Referring to FIGS. 5A to 5T for series of cross sectional views toillustrate the manufacturing processes for making a device structure asshown in FIG. 3. As will be understood from the disclosures made inthrough the descriptions of the manufacturing steps, the processes onlyrequire three masking steps because of a beneficial Self-AlignedStructure. The processes start with a silicon substrate that has ahighly P+ doped bottom 205 to function as a source terminal. The P+doped bottom layer 205 may be doped with Boron to have a resistivity of3 to 5 mOhm-cm or a lower resistivity. A P− epitaxial layer 210supported on the substrate 205 with a thickness ranging from 2 to 7micrometers. In one embodiment, the P-type epitaxial layer is doped witha low dosage of 5E14 to 5E15 for 20-60 volts application. In anotherembodiment, the epitaxial layer 210 may be an N− doped layer.Optionally, a blanket shallow N-type implantation is performed to forman N-drift region 215 followed by a thick oxide deposition to form anoxide layer 220 as a hard mask with a thickness ranging from 0.5 μm to1.5 μm. A densification process by applying an elevated temperature iscarried out as an optional step. In FIG. 5B, a first mask, i.e., atrench mask (not shown), is applied to carry out a hard mask etchfollowed by a silicon etch up to 70% to 130% depth of the N-well orN-epitaxial layer thickness. The process may follow with an isotropicetch and these etch processes open a trench through the hard mask layer220, the drift region to extend the trench into the epitaxial layer 210.The a N-link region implant is carried out by implanting phosphorousions at quad tilt or double ±7 degree tilt angles with a dosage rangingbetween 1E12 to 1E13 to form the N-link regions 225 surrounding thetrench sidewalls and the trench bottom. Other angles of ionimplantations ranging from 4 degrees to 15 degrees or more may be usedas well, depending on the dimensions and geometry of the structure. InFIG. 5C, a conformal oxide deposition of an oxide layer 230 is depositedfollowed by an anisotropic etch as shown in Fig.5D to remove the top ofthe conformal oxide layer while leaving a thick sidewall oxide layer 230covering the trench sidewalls. In FIG. 5E, a selective silicon channeletch is performed to etch a depth of 0.3 to 1.0 μm from the trenchbottom into the epitaxial layer followed by carrying out an isotropicsilicon etch to further extend the trench by a depth of 0.3 to 1.0 μm asan optional step. In FIG. 5F, a sacrificial etch is first performedfollowed by a thermal oxide growth process to form a gate oxide layer235 covering the lower portion of the trench sidewalls. In FIG. 5G, azero tilt boron channel implant is carried out through the trenches withan implant dosage ranging between 5E12 to 1E14 to form a trench bottombody region 240 forming a channel along the sidewalls of the trenches.Then an elevated temperature of approximately 1050 C is applied with anitrogen gas N2 for about thirty minutes to drive the trench bottom bodyregion 240 forming a channel along the sidewalls of the trenches.

In FIG. 5H, a tilt lower dose boron implant through the bottom portionsof the trench sidewalls is performed to complete the channel implant forthreshold and punch through adjustments. The thick oxide layer 230 onthe drain sidewalls functions as a mask for this channel implant. InFIG. 5I, an anneal operation is performed with nitrogen gas N2 at anelevated temperature ranging from 950 to 1100° C., followed by a sourceimplant with arsenic ions at a dosage ranging between 1 to 6E15 with animplanting energy of 40 to 160 Kev with zero tilt implant angle isperformed through the trenches to form the trench bottom source regions245. Then a source anneal operation is performed as an optionalprocessing step. In FIG. 5J, a sacrificial oxide strip is performed toremove the oxide layer followed by a gate oxide growth then apolysilicon layer 250 is deposited followed by an in-situ implant todoped the polysilicon layer 250. Then an oxide layer 255 is deposited ontop of the polysilicon layer. In FIG. 5K, an anisotropic oxide etch isperformed to remove the oxide layer 255 from the top of the polysiliconlayer 250 leaving only the oxide layer 255 covering the polysiliconlayer 250 in the trenches. In FIG. 5L a polysilicon anisotropic etch iscarried out to remove the polysilicon layer 250 outside of the trenchesand leaving only the polysilicon layer 250 to function as sidewall gatesinside the trenches attached to the trench sidewalls covered by theoxide layer 255. In FIG. 5M, an optional isotropic silicon etch isperformed to pull back the polysilicon in the trench bottom slightlyunder the trench spacer layer 255 followed by a conformal oxide layer260 with a thickness ranging between 500 to 2000 Angstroms is depositedfor covering the top surface of the device. Then a polysilicon oxidationanneal at an temperature ranging from 850° C. to 1050° C. is carried outto grow an oxide layer of thickness ranging from 50 to 600 Angstromsfollowed by an oxide densification process. In FIG. 5N, an anisotropicoxide etch is performed to remove the oxide layer 260 from outside ofthe trenches and the oxide layer 260 that covers the bottom of thetrenches to expose the contact to the body regions 240 encompassing thesource region 245 and forming a channel along the sidewalls of thetrenches. The anisotropic etch is controlled as a time etch without overetching the oxide layer thus leaving the oxide layer 260 in the fieldregions covering the bottom portions of the polysilicon gates 250.

In FIG. 5O an anisotropic silicon etch is carried out to further etchthe trench bottom with a etch depth ranging from 0.1 to 0.5 μm for atypical structure. Then a BF2 or boron blanket implant is performed toform a shallow contact region 265 immediately below the etched trenchbottom followed by an implant annealing with a rapid thermal anneal(RTA) operation at 900 to 1100 C. for ten to sixty second with NitrogenN2 gas. In FIG. 5P, a silicide deposition with Ti, Co, or W is performedfollowed by a RTA process. Then a salicide wet etch is carried outfollowed by a RTA process to form the salicided contact layer 270 at thebottom of the trench in immediate contact with the shallow contactregions 265. This process can optionally carried out by a tungstendeposition followed by etch back to form the tungsten plug as thebody/source contact because the tungsten is compatible with the hightemperature processing steps. Alternately, the formation of a WSix layer270 is another option as a high temperature stable salicide layerwithout requiring the salicidation RTA processes by just tungstendeposition followed by etching back. In FIG. 5Q, an undoped thin oxidelayer is deposited followed by a BPSG layer 275 deposition then a lowtemperature reflow compatible with the silicde structure 270 isperformed at 850 to 900 C. In FIG. 5R, a passivation layer of PSG andSixNy or Si-rich nitride layer or oxynitride or silicon nitride layer280 is deposited. In FIG. 5S, a drain and gate contact mask, i.e., asecond mask (not shown), is applied. A nitride/oxide etch is performedto remove the passivation layer 280 and the oxide layers from the drainand gate contact areas. The process may proceed with an optionalisotropic and anisotropic etch to develop sloped sidewalls. Then ashallow drain contact implant with N+ dopant of arsenic or phosphorousions is carried out to form the N+ drain contact regions 285 followed byRTP annealing process with Nitrogen gas N2 at a temperature rangingbetween 900 to 1050 C. for less than one minute. In FIG. 5T, a thickmetal layer 290 is deposited followed by etching and patterning themetal layer into gate and drain metal contacts by applying a metal maskas the third mask. Then an alloying process is performed to complete thefabrication processes.

According to above device configuration, a low manufacturing cost isachieved because a lower effective die cost can be achieved by using asmall die and this reduced cost is able to offset the highermanufacturing costs. Most importantly, a low source inductance isachieved through the use of a substrate source contact while minimizingthe source resistance by implementing the source-body short structuredistributed over the device. Furthermore, a small pitch of the device asdescribed above further reduces the specific-on-resistance (Rsp) for agiven operating voltage. The device configuration is convenientlyscalable for compatible designs and operations adaptable to devices thatrequire a range of high and low voltages. The device further providesrugged and reliable performance with reduced possibility of latch up,reduced hot carrier injection, and capability to handle peak generationaway from gate oxide, etc., because of the distributed body contactthrough the source-body short structure. Therefore, an invertedground-source trenched FET device is disclosed that allows for verticalcurrent through vertical channel. The controllable drift length of thedrift region implemented with the vertical channel enable themanufactures of small and scalable cell pitch. With the source contactat the bottom of the trench in direct contact with the highly dopedsubstrate reduces the source resistance. There is no longer a need fordeep resistive sinker region or trench contact as that usuallyimplemented in the conventional bottom source FET devices.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artafter reading the above disclosure. Accordingly, it is intended that theappended claims be interpreted as covering all alterations andmodifications as fall within the true spirit and scope of the invention.

1. A method for manufacturing an iT-FET semiconductor device on asemiconductor substrate having a doped bottom layer functioning as abottom source region, the method further comprising: opening a trench inthe semiconductor substrate followed by doping a body region surroundinga lower portion of the sidewalls of the trench and below a bottomsurface of the trench and doping a source region below the bottomsurface of the trench encompassed in the body region; depositing apolysilicon layer into the trench followed by etching a central hole inthe polysilicon layer in the trench for forming a trenched gate as thepolysilicon layer attached to the trench sidewalls followed by doping abody contact region below the source region through the central holewherein the trenched gate on the sidewalls controlling a verticalchannel formed along said trenched gate in said body region forconducting a current vertically between a top drain electrode to thebottom source region.
 2. The method of claim 1 further comprising:depositing into the central hole in the polysilicon layer in the trenchwith an insulation layer.
 3. The method of claim 2 further comprising:etching a central portion of the insulation layer to expose a centralportion of the bottom surface of the trench then etching a source-bodycontact hole through the source region through the exposed bottomsurface of the trench before doping the body contact region below thesource region.
 4. The method of claim 3 further comprising: depositing aTi, Co, or W followed by a rapid thermal anneal (RTA) and a salicide wetetch form a salicided contact layer in the source-body contact hole inimmediate contact with the source region and the body contact region. 5.The method of claim 1 further comprising: doping a vertical linkingregion next to an upper portion of the trench sidewalls linking to andabove the body region for linking to the channel region.
 6. The methodof claim 5 further comprising: doping a top drift region above thevertical linking region and forming a drain contact region encompassedin the top drift region for contacting a top drain electrode above a topsurface of the semiconductor substrate.
 7. The method of claim 6 furthercomprising: depositing insulation and passivation layer to top of thetop surface of the semiconductor substrate on top of the drain contactregion and the drift region and opening drain contact openings and gateopenings.
 8. The method of claim 7 further comprising: depositing ametal layer on top of the insulation and passivation layers forcontacting the drain contact region and gate contact regions followingby patterning the metal layer into drain contact and gate contact pads.9. The method of claim 1 wherein: the step of opening the trench in thesemiconductor substrate further comprising a step of first opening ashallow trench and covering the shallow trench with a conformalinsulation layer followed by an anisotropic etch to form spacer layer onsidewalls of the shallow trench then etching through a bottom surface ofthe shallow trench using the spacer as a mask to form the trench for thetrench gate of a greater depth into the semiconductor substrate.
 10. Themethod of claim 9 further comprising a step of implanting a drift-linkregion before the formation of the spacer.
 11. The method of claim 1wherein: the method of depositing a polysilicon layer into the trenchfollowed by etching a central hole in the polysilicon layer in thetrench further comprising a method of depositing a polysilicon layerfollowed by a depositing an oxide layer overlaying the polysilicon layerthen followed by an anisotropic oxide etch and an anisotropicpolysilicon etch.
 12. The method of claim 1 further comprising:manufacturing the iT-FET semiconductor device on the semiconductorsubstrate comprising an epitaxial layer lightly doped of a firstconductivity overlaying a substrate layer heavily doped of the firstconductivity.
 13. The method of claim 12 further comprising: blanketimplanting a shallow drift layer on a top portion of the epitaxiallayer.
 14. The method of claim 1 further comprising: manufacturing theiT-FET semiconductor device on the semiconductor substrate comprising anepitaxial layer lightly doped of a first conductivity overlaying asubstrate layer heavily doped of a second conductivity opposite thefirst conductivity.